1-Fertilization Definition: It is the process by which the sperm of the male & ovum of the female meet and fuse. Site: In the ampullary part of the uterine tube, for 2 reasons: It is close to the ovary. It is the widest part of the uterine tube. It is small (with a length of about 50, and highly motile. It consists of head, neck and a motile tail. The head contains the nucleus that is covered by The acrosome (an organelle containing enzymes). There are two types of sperms according to the chromosomal contents i.e. the Y- bearing sperm (having 22 autosomes + Y) And the X bearing sperm (having 22 autosomes +X). It has large size, immotile, covered by zona pellucida and corona radiate. Its cytoplasm is abundant (containing yolk granules for nutrition of the embryo during the first week of development). Its nucleus contains 22 chromosomes + one X chromosome. How the sperms reach the site of fertilization? 1. By movement of their tail. 2. By the movement of uterine cilia. 3. By chemo attraction. How the oocyte reaches the site of fertilization? 1. By the movement fimbria of the uterine tube. 2. By peristaltic movement of the uterine tube. Capacitation: the glycoprotein coat is removed from the surface of the sperm's acrosome. It takes about 7 hours. Only the capacitated sperms can penetrate the corona radiata. Acrosome reaction: It occurs after capacitation where proteolytic enzymes as acrosin, esterases, hyaluronidase, and neuraminidase are liberated in order to penetrate the zona pellucida. 1. Passage of sperm through the corona radiate. 2. Penetration of the zona pellucida. 3. Fusion of the oocyte and sperm cell membranes to form the zygote (the unicellular embryo). 1. Restoration of the diploid number of chromosomes (46 chromosomes). 2. Determination of the embryo's chromosomal sex (the female is 46,XX and the male is 46,XY). 3. Stimulation of cleavage (mitotic cell divisions of the zygote). This method is used in cases of infertility where the ovaries are stimulated by high doses of hormones to produce many ova in the same ovarian cycle (ovarian stimulation). Then several ova are withdrawn from the Graffian follicles of the ovary of the wife before ovulation. They are then placed with the husband's sperms in a petri-dish containing nutrient medium. So fertilization occurs outside the mother's uterine tube (in vitro). Two or three of the resulting zygotes are placed back in the uterus (embryo transfer ) after 3 days of fertilization. Intracytoplasmic sperm injection (ICSI) It is the method of choice in cases of infertility due to the male factor (severe oligospermia). It implies the same process as IVF except that the best sperm is selected and injected into the ovum cytoplasm. Definition : It is the repeated mitotic divisions of the zygote, resulting into a rapid increase in the number of cells that are called blastomeres. Site: The uterine tube medial to the ampula. a- Morula: It has 16 cells (blastomeres). It has mulberry appearance. It is surrounded by Zona pellucida. It enters the uterus nearly 3 Days after fertilization. b- Blastocyst formation: As morula reaches the uterine cavity, fluid from the uterine cavity penetrates the zona pellucida and accumulates in the inter-cellular spaces. -A single cavity is formed and called blastocele. -The morula after the formation of blastocele is called blastocyst. -The blastocyst consists of inner cell mass (it will form the future embryo; so it is called embryoblasts) and outer cell mass (future trophoblast & placenta). The zona pellucida disappears allowing for implantation. Definition: Penetration of the blastocyst into the superficial (compact) layer of the endometrium. Time: Implantation occurs at the 6th day after fertilization and is completed about the 11th day. Site: The normal site is the endometrium of the posterior wall of the fundus of the uterus in or near the middle line. The endometrium after implantation is called decidua. - While floating freely in the uterus, the embryo derives nourishment from secretions of the uterine glands. - About 6 days after fertilization, the blastocyst at the inner cell mass side (embryonic pole) attaches to the endometrium. - The trophoblast proliferates rapidly and becomes differentiated into two layers: A. an inner cellular layer of cytotrophoblast. B. an outer multinucleated protoplasmic mass with no cell boundaries called syncytiotrophoblast - Syncytiotrophoblast forms fingerlike processes that extend into the endometrium and the connective tissue stroma. It produces enzymes that erode the maternal tissues so enabling the blastocyst to burrow into the endometrium. This implanted blastocyst gets its nourishment from the eroded maternal tissues. Definition : It is the compact layer of the endometrium after implantation of the blastocyst. 1. Decidua basalis (part of endometrium between the blastocyst & the myometrium ). 2. Decidua paritalis (endometrium covers the wall of the uterus). 3. Deciduas capsularis (endometrium between the blastocyst & uterine cavity). 4. Decidua marginalis (endometrium surrounding the site of implantation). 1. Uterine ectopic pregnancy: a. At the cornu of the uterus (the site of attachment of the uterine tube) leading to early abortion. b. At the lower uterine segment leading to placenta previa. c. Cervix, leading to cervical pregnancy and early abortion. mesentry tube ovaryInternal os It is also called ectopic pregnancy. It might result in death of the embryo or early abortion with severe internal hemorrhage. 1,A 2,C 1,C 1,B 2,A 2,B 2. Extra uterine ectopic pregnancy: a. The commonest site is in the Fallopian tube leading to tubal pregnancy that leads to early abortion or tubal rupture with severe internal haemorrhage. b. Ovary ( ovarian pregnancy ), broad ligament or omentum (rare). c. Peritoneum of Douglas pouch ( abdominal pregnancy ). Definition: Implantation of the blastocyst in the lower segment of the uterus close to the internal os. Thus the placenta will preceed the fetus at delivery (normally, the fetus is the lowermost and fills the lower segment). Previa = at the front of the fetus. Types of placenta previa: 1. Placenta previa parietalis : The placenta lies in the lower segment away from the internal os of the cervical canal. 2. Placenta previa marginalis : The placenta covers partially the internal os. During labour, it is shifted upwards away from the internal os. 3. Placenta previa centralis : it lies in the lower segment and completely covers the internal os. During labour, it leads to ante-partum Hge. It may lead to malposition of foetus. Prof.: Dr. Wafaa Abdel-Rahman